<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>
  <!-- 事件代理 -->
  <ul class="box">
    <li>1</li>
    <li>2</li>
    <li>3</li>
  </ul>

  <script>
    // 事件代理
    let ul = document.getElementsByClassName('box')[0]
    ul.addEventListener('click', function (e) {
      console.log(e.target.tagName);
      if (e.target.tagName === 'LI') {
        e.preventDefault()
        console.log(`我是第${e.target.innerText}个li标签`);
      }
    })

    
  </script>
</body>

</html>